I am not sure about how parallel entry into hold is done in bigger aircrafts like 737 in raw data mode (VOR mode on Nav Display)
Take example of Cochin Intl Airport ILS-Z via overhead (as shown in attachment)
suppose aircraft is approaching overhead on radial 040. Now once overhead Do we turn right immediately or after certain time (like 15 seconds so that we parallel)? on heading 281 (+- wind correction) and then fly for one minute or less? Then fly direct to VOR following the VOR Bearing Pointer shown on ND. Then turn left overhead and enter out-bound. Fly for one minute. Thus continue hold. When cleared for approach on inbound leg approaching overhead arm VOR LOC and turn so that you proceed outbound on 101 radial.
Is there any thumb rule as to how many miles before overhead we need to turn to take care of aircraft momentum. Typically people follow 10% of Ground Speed. But my observation is it doesn't really work out every time